Photoresist is an organic polymer which becomes soluble when exposed to light. Photoresist is used in many applications within various industries, such as the semiconductor, biomedical engineering, holographic, electronics, and nanofabrication industries. As an example, photoresist is used to help define circuit patterns during chip fabrication in the semiconductor industry. The use of photoresist prevents etching or plating in the area the photoresist covers (this is also know as resist).
The removal of photoresist, commonly known as “stripping” is preceded by plasma ashing, etching, or other manufacturing steps. These steps can degrade or carbonize the photoresist and leave a photoresist reside that is difficult to remove by current stripping methods. In particular, ion implantation with a dose of 3×1015 ions/cm2 or higher creates a photoresist exhibiting a hard outer crust covering a soft core. FIG. 1A illustrates a cross-sectional view and FIG. 1B illustrates a top view of a photoresist exhibiting a hard outer crust 40′ caused by ion implantation. As illustrated in FIGS. 1A and 1B, the hard outer 40′ crust may be on the order of 200 to 300 Å thick.
FIG. 2 is a cross-sectional view illustrating the ion implantation step. FIG. 2 illustrates a substrate 110, a gate electrode 10, an insulation film 11, and n-region of a source/drain region 20, a spacer 30, a photoresist pattern 40, and a well 50. When the photoresist pattern 40 is exposed to ion implantation 45, a hard outer crust 40′ is formed on the photoresist pattern 40.
Residue may also be a problem. FIG. 3A illustrates a cross-section view and FIG. 3B illustrates a top view of a photoresist exhibiting residue after an etching process or a chemical mechanical polishing (CMP) process. FIG. 3A illustrates a substrate 110, an etched player 60, a photoresist pattern 70, and a hard outer crust 70′, which is formed when the photoresist pattern 70 is exposed to ion implantation 75, FIGS. 3A and 3B illustrate residue 80 and an organic defect 90.
Conventionally, photoresist has been removed by a plasma ashing process followed by a stripping process. The plasma ashing process utilizes 02 plasma which may cause damage to the sublayer and thereby degrade the electrical performance of the underlying semiconductor device. The stripping process requires high quantities of toxic and/or corrosive chemicals to remove photoreactive polomers or photoresist from chip surfaces.
In order to overcome these problems, other stripping methods have been developed including organic and/or inorganic stripping solvents with supercritical carbon dioxide (SCCO2) or ozone (O3) gas. Techniques which remove resist using SCCO2 utilize a densified CO2 cleaning composition which includes CO2 and at least one cosolvent such as a surfactant, alcohol, or amine. However, the methods utilizing SCCO2 and a cosolvent are incapable of dissolving a hard outer crust of a photoresist caused by ion implantation.
A second method for removing photoresist or other organic material from a substrate such as a semiconductor wafer includes partially immersing the substrate in a solvent, for example, deionized water, in a reaction chamber, injecting an oxidizing gas, for example, ozone, into the reaction chamber and rotating or otherwise moving the substrate through the solvent to coat a thick film of solvent over the organic component on the substrate surface and expose the solvent-coated component to the ozone gas to remove the organic material from the surface. Again, the resist removal techniques utilizing ozone are incapable of dissolving a hard outer crust caused by an ion implantation step. FIG. 4 illustrates a failure of a resist removal techniques using ozone to remove a hard outer crust of the photoresist caused by ion implantation with a dose of 3×1015 ions/cm2 or higher.